In part A (10 patients), G-CSF is given s.c., divided in two daily doses starting at day 4 until collection of stem cells. Plerixafor is given as an i.v. application on day 8 in the dose of 240 microg/kg b.w. Stem cell collection is initiated 4 hours later at day 8, if at least 20 x 103 of CD34+ cells / ml peripheral blood are detected. In case of insufficient collection, the procedure is repeated at day 9, including repetition of plerixafor application.